I have thought that Quake4-demo would be a fine computer game for my son sons (12, 10 and 2 years, they have a 5 years old sister also but I do not count her with). The only problem is their father who is a clergyman. He does not allow the sons to play any FPS were the targets are human beings.

I have played Quake myself a little but I have not been able to proceed far. But I have realized that the aliens I meet have much the same with human being except the spider one sees in the beginning. The behavior of the aliens is also quite natural and human, they only try to defend their country

So should we not meet the aliens with friendly attitude than at ones shooting when they appear? Or is there in Quake an option to use words or The Book instead of guns

Ha!, here in holland the game is rated 18+....... so you have 2 be over eightteen years old to even watch parts of it. Prolly due to gore etcetera
Quake3 was rated 18+ already too dont know bout quake2 or quake1...